Polymer semiconductor device comprising at least a rectifying function and method for making same

ABSTRACT

A semiconductor device made of polymer. The device includes at least one rectifying function formed by a layer of polymer between a first and a second electrode. The layer of polymer forms a host matrix for polar molecules with the polar molecules being electrically oriented in a direction perpendicular to the electrodes. The electrical charges of the polar molecules of the same sign are directed towards the same electrode. The method of producing such a device is also included.

BACKGROUND OF THE INVENTION

The invention relates to a semiconductor device made of polymer thatincludes at least one rectifying function. In particular it relates todiodes and notably photovoltaic and electroluminescent diodes. It alsorelates to devices such as transistors.

DISCUSSION OF THE BACKGROUND

The use of polymers to produce semiconductor devices is technicallyrather interesting. In effect, the polymers can be formed by a wetmethod from a solution, which leads to techniques which are easy toimplement, that are low cost and which are compatible with othertechniques.

In order to produce semiconductor devices such as electroluminescentdiodes and photovoltaic cells, it is usually appropriate to create ajunction. This can be a Schottky junction obtained by bringing a dopedsemiconductor into contact with a metal having a rectifier contact withthe semiconductor used. It may also be a pn junction obtained by placinga p type semiconductor at the side of an n type semiconductor. Thejunction is called a homo-junction if the semiconductor material is thesame for the whole of the junction. In the contrary case, one speaks ofa hetero-junction.

It is known to use polymers to produce these two types of diode(Schottky and pn junction). As a function of the type of conductivityrequired, p or n, it is preferable to chemically dope the polymer withatoms (or molecules) that are respectively acceptors or donors ofelectrons.

A disadvantage of Schottky diodes produced by the juxtaposition of ametal and a polymer is their short life. This is due to the diffusion ofthe metal into the polymer where the two materials are in contact,because of the difference in the electrochemical potential that existsbetween these two materials.

Logically, a pn junction should allow this disadvantage to be remedied.It is produced by the juxtaposition of a type p polymer and a type npolymer. However, it is extremely difficult to produce such pn junctionssince the choice of the different polymers is not always compatible withthe operational imperatives. Furthermore, type n type polymers are notvery common and are often unstable to oxygen.

Another problem inherent to polymer diodes of both of these types(Schottky and pn) is linked to the small breadth of the depletion layerat the junction which is less than 20 nm. So as to avoid short circuitsbetween the electrodes, the devices made up of thin layers of polymerare produced with a thickness greater than or equal to 100 nm. As themobility μ of the charges within the organic components is a functionthat increases rapidly with the internal electric field E of thesemiconductor in accordance with the empirical law

μ=μ_(o) ·exp[(E/E_(o))^(P)]

where the exponent p is close to 0.5 and as the internal field E is onlylarge within the depletion layer, the electrical charges do not passwell in polymer semiconductor devices of the known art. This leads tolow efficiency for these devices.

SUMMARY OF THE INVENTION

This invention allows these disadvantages to be remedied. It consists ofcreating a rectifying homo-junction gradient equivalent to a pn junctionin a single thin layer of polymer which is used as a host matrix forpolar molecules orientated in an appropriate manner. The result is asignificant increase in the mobility of the carriers within the entirethickness of the layer which leads to a uniformly distributed depletionlayer. This principle in a significant way, improves the performance ofthe devices with a junction such as electroluminescent diodes,photocells and transistors produced from polymers.

Therefore a first subject of this invention consists of a semiconductordevice made of polymer that includes at one rectifying function,characterized in that the function is produced by a layer of polymerbetween first and second means that form electrodes, the layer ofpolymer constituting a host matrix for polar molecules, the polarmolecules being electrically orientated in a direction perpendicular tothe first and second means forming the electrodes, the electricalcharges of the polar molecules of same sign being directed towards thesame means that form an electrode.

A second subject of this invention consists of a method of producing apolymer semiconductor device that includes at least one rectifyingfunction, characterized in that it includes the following steps:

formation of a layer based on polymer and including polar molecules, thepolymer constituting a host matrix for the polar molecules,

orientation of the polar molecules in the host matrix so that theelectrical charges of the polar molecules of same sign are directed tothe same side.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other advantages andparticular features will become apparent on reading the description thatwill follow, given by way of a non-limitative example and accompanied bythe appended figures among which

FIG. 1 is a current-voltage diagram of a structure comprising a layer ofpolymer placed between two electrodes,

FIG. 2 is a diagram representing the variation in the height of thepotential barrier between an electrode and the polymer layer of astructure according to the invention as a function of the rate oforientation of the polar molecules,

FIG. 3 is a diagram representing the mobility of the electrons in astructure according to the invention before polarization and for twoopposite values of the polarization field,

FIG. 4 represents a side view of a photocell according to thisinvention,

FIG. 5 is a perspective view of a photocell device according to thisinvention,

FIG. 6 represents a side view of an electroluminescent diode accordingto the present invention.

FIG. 7 represents a side view of a field effect transistor according tothe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The diagrams in FIGS. 1, 2 and 3 allow one to illustrate the principlewhich lies at the base of this invention. They relate to a symmetricaldiode made up of a thin film of polymer semiconductor situated betweentwo electrodes of the same kind and including polar organic molecules.The thin film is a copolymer (MMA-DR1) 50/50 which will be definedbelow, the MMA playing the role of host matrix and the DR1 constitutingthe polar molecules. The electrodes are made of aluminum.

Initially, the structure constituted in this way is perfectlysymmetrical as its current-voltage characteristic taken at ambienttemperature and represented by curve 1 in the diagram in FIG. 1 shows.The principle which forms the basis of this invention consists ofinducing a rectifying diode function of the pn type by modification ofthe nature of the polymer layer situated between the electrodes. Themodification is carried out by the orientation of the polar molecules inthe host matrix. By applying a static electric field to the thin filmand simultaneously bringing this thin film to a temperature close to itsvitreous transition temperature Tg, the polar molecules quantitativelyorientate themselves in accordance with the electric field. Thisorientation is frozen by maintaining the static electric field duringthe cooling phase of the structure. It is possible to directly link theinternal field induced in the polarized structure to the rate oforientation of the polar molecules.

The effect of the orientation of the polar molecules is apparent fromthe curves on the I f(V) diagram in FIG. 1. Curve 1 showing thecurrent-voltage characteristic before polarization of the structure,curve 2 shows the current-voltage characteristic of a similar structureobtained after polarization by 5 V, at a temperature of 130° C. for 10minutes, curve 3 shows the current-voltage characteristic of a similarstructure obtained after polarization by 10 V, at a temperature of 130°C. for 10 minutes and curve 4 shows the current-voltage characteristicof a similar structure obtained after polarization by 15 V, at atemperature of 130° C. for 10 minutes. The rectifying effect, afterpolarization at a temperature close to the vitreous transitiontemperature is clearly apparent on the diagram in FIG. 1.

By taking the classical model for the Schottky diode for thesemiconductors, one can make a theoretical adjustment to thecurrent-voltage curves by using the usual parameters:

I=I _(S) [exp(qV/nkT)−1]

with

I_(S): saturation current

V: applied voltage

n: ideality factor

q: charge of the electron

k: Boltzmann constant

T: absolute temperature

In this way, for each of the values of the polarization of thestructure, the saturation current can be estimated. By analogy withmineral semiconductors, one can then calculate φ_(b), themetal-semiconductor barrier potential through the following equation

I _(S) =AR*T ² exp(−qφ_(b/kT))

with

A: area of the diode

R*: Richardson constant

R*=4πm _(e) qk ²/h³

The value φ_(b) is compared with measurements of the rate of orientationcarried out by generation of a second harmonic. These measurements ofthe rate of orientation can be carried out as described in the thesis ofG. GARDET entitled “Non-linear optical properties of polarized polymers:a study of the chromatic dispersion of their electro-optical coefficientby modulation of the reflectivity” and supported by The University ofParis XI in 1993. The variation in the height of the metal/organicsemiconductor potential barrier is thereby linked to the rate oforientation of the molecules in the matrix of the polymer.

FIG. 2 shows that, by orientation of the molecules, a function has beenproduced equivalent to a pn junction with an internal potentialdifference close to 0.2 eV. There is a homo-junction gradient spreadover the entire thickness of the film of polymer.

In FIG. 1, it should also be noted that in addition to the rectifyingeffect (asymmetry of the characteristic), the conductivity of the diodein the on state (diode positively polarized) is significantly increasedafter orientation of the molecules. This effect is confirmed bymeasurement of the flight time. This measurement permits thedetermination of the type of conduction of a material (n conduction ifthe electrons are the major carriers, or p if the holes are) and themobility of the charges.

The diagram in FIG. 3 shows the results obtained for the mobility of theelectrons before and after orientation of the molecules for two oppositevalues of the polarization field applied at 130° C. The mobility on thediagram in FIG. 3 is drawn as a function of the electric field E appliedduring the measurement. The law of mobility

μ=μ_(o) ·exp[(E/E _(o))^(1/2)]

is verified. The increase in the mobility of the electrons isasymmetric. It goes in the direction of the rectifying effect induced.

In the diagram in FIG. 3, the mobility μ of the electrons is on they-axis and the electric field E is on the x-axis. In the diagram in FIG.3, the points marked with triangles represent the mobility of theelectrons before polarization by an electric field, the points markedwith squares represent the mobility of the electrons after polarizationresulting from the application of a negative voltage of 100 V, for 5minutes at 130° C., the points marked with solid circles represent themobility of the electrons after polarization resulting from theapplication of a positive voltage of 100 V, for 5 minutes at 130° C.

The diagram in FIG. 3 shows that, by orientation of the molecules, theelectronic mobility μ_(o) in the on direction without an appliedexternal field is increased by a factor of 4. This effect is fundamentalfor the performance of semiconductor devices of the photocell type andelectroluminescent diode type.

It is advantageous to use, as polar molecules, active organic moleculesderived from the field of non-linear quadratic optics. They are of the“push-pull” type, that is to say they have both an electron donor group(of the amino type) and an electron acceptor group (of the nitro type),separated from one another by one or more groups comprising conjugated πelectron systems, which are therefore capable of being displaced overseveral atoms (diazobenzene in the case of the DR1 molecule, forexample). This type of molecule is fully described in “MolecularNonlinear Optics: materials, physics and devices”, published by J. ZYSSat Academic Press Inc. (1994), “Organic Nonlinear Optical Materials”,Vol. 1, by Ch. BOSSHARD, K. SUTTER, Ph. PRETRE, J. HULLIGER, M.FLORSHEIMER, P. KAATZ, P. GUNTER, published by Gordon and BreachPublishers, (1995) and in the document FR-A-2 732 482 that discloses a“Method of manufacturing structures made of transparent, organicpolymers auto-organized for the conversion of an optical frequency”, byF. CHARRA, C. FIORINI, A. LORIN, J-M. NUNZI and P. RAIMOND.

An example of a polar molecule is Disperse Red 1 (DR1):

4-[N-(2-hydroxyethyl)-N-ethyl]-amino-4′-nitroazobenzene (Aldrich,recrystallized) which has the following chemical structure:

This molecule can be used in a photocell as a photo-generator ofcharges.

Another example of a polar molecule is DCM:4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyrane(Exciton) which has the following chemical structure

This molecule can be used in an electroluminescent diode as an emitterof red light at 620 nm.

The polymer that is suitable to use is advantageously soluble. It musthave significant carrier mobility after the inclusion of activemolecules by doping or by grafting onto the main chain. It may be asemiconductor polymer such as those described in the “Handbook ofConducting Polymers”, published in two volumes by SKOTHEIM in 1986 atMarcel Dekker. The soluble derivatives of polythiophene (PT),polyparaphenylene (PPP) and polyparaphenylenevinylene (PPV) areexamples. It may also be one of a number of polymers that becomesemiconductors through doping, for example polymethyl methacrylate(PMMA), polyvinyl carbazole (PVK), polycarbonate (PC), polystyrene (PS)and polyvinyl chloride (PVC).

For example, polymethyl methacrylate (PMMA) is used as an isotropicmatrix polymer that is optically inactive and transparent in the visibleand near infra-red. Its chemical formula is as follows

The active molecule can be chemically attached (grafted) to the polymer.Hence, the copolymer DR1-MMA grafted with 50 mol. % of chromophors(50/50 DR1-MMA) is obtained by free radical polymerization from asolution of methyl methacrylate (MMA) andN-ethyl-N-(methacryloxyethyl)-4′-amino-4-nitroazobenzene (derivative ofDR1). This material has a vitreous transition temperature close to 132°C. Its formula is as follows:

The semiconductor device according to this invention allows one toproduce a photocell (photovoltaic cell). A traditional way of producinga photocell is described in the article “organic Solar Cells” by D.WOHRLE and D. MEISSNER, published in Advanced Materials, Vol. 3 (1991),No. 3, pages 129-138.

The photocell according to the invention is shown diagrammatically inFIG. 4. It includes a transparent substrate 10, for example, made ofglass, that supports a transparent electrode 11, for example made ofmixed oxide of tin and indium (ITO electrode). A layer of organicsemiconductor 12 constituted by a polymer that includes polar moleculesis between the transparent electrode 11 and a metal electrode 13, forexample, an aluminum electrode. The electrodes 11 and 13 arerespectively connected to output terminals 14 and 15. In operation, thelight indicated by arrows in FIG. 4 is absorbed through the transparentface of the photodiode. Electrical charges are then photo-generatedclose to the interface between the transparent electrode 11 and thepolymer layer 12. The electric field inside the structure, which isinduced by the orientation of the polar molecules contained in thepolymer host matrix, encourages the separation of the charges and themovement of one of the carriers towards the aluminum electrode. Acurrent is then generated.

For an embodiment more capable of industrial production, a substrate canbe used that is made up of a standard sheet of glass, covered with ITO(Conductin 013 A treatment from Balzers) of resistance equal to 13 Ω/□,and of thickness equal to 1 mm. The conductive coating is then etched bylaser attack in accordance with the configuration illustrated in FIG. 5where reference number 20 designates the sheet of glass. The laserablation divides the conductive and transparent coating into three parts21, 22 and 23. After cleaning with a traditional detergent (TDF4), theparts 21, 22 and 23 are rinsed with distilled water and then subjectedto several cycles of ultrasound treatment. The substrate made up of thesheet of glass and its conductive coating is then heated in an oven to400° C. in such a way as to remove by pyrolysis any possible residualorganic impurities.

The organic film is obtained by centrifuging the polymer solution ontothe substrate (trammel deposition). The thickness of the layer and itshomogeneity depend on the rotation parameters of the trammel and theviscosity of the solution. The apparatus is regulated in both ways.

Films of thickness 0.13 μm are obtained from a solution of 50/50(MMA-DR1) copolymer at 30 g/l in 1,1,2-trichloroethane. The solution isfiltered at the moment of deposition through a 0.5 μm filter. Thecentrifuging parameters are the following

Deposition phase:

first acceleration

200 rpm/sec

first cycle: 110 rpm

for 10 sec,

Drying Phase:

second acceleration

300 rpm/sec,

second cycle

5000 rpm for 50 sec.

After deposition, the substrate covered with the thin film is cured for15 minutes at 80° C. which allows any residual solvent to be removed.Measurement of the thickness is carried out with the help of a Veecomodel Dektak 3ST profile meter.

The left part of the thin film corresponding to parts 22 and 23 is thenpartially scraped in order to lay bare those parts 22 and 23 which willbe used as electrical contact points. Similarly, the extreme right partof the thin film is also scraped to facilitate making contact.

Then, as can be seen in FIG. 5, electrodes 24 and 25 made of aluminumare deposited on the thin organic film 29 by evaporation through a mask.The vaporization is carried out under vacuum at 1.33×10⁻⁴ Pa (10⁻⁶Torr). It allows the simultaneous deposition of conductive strips 26 and27 that provide the electrical connection between electrodes 24 and 25and the contact points 22 and 23 respectively. Two photocells areobtained with a unitary surface area of 38 mm² and having a commonelectrode formed by the conductive part 21.

The device obtained is then brought to a temperature of 130° C. and avoltage of 15 volts is applied to each diode for 10 minutes. Thentemperature regulation of the device is stopped while all the timekeeping the same polarization voltage applied. The temperature of thedevice is allowed to fall again to 25° C. in 30 minutes. The staticapplied electric field is then switched off.

The effect of the colorant DR1 is that the major charge carriers in the50/50 MMA/DR1 copolymer are the electrons (type n material). Theirmobility is therefore increased by orientating the DR1 chromophors withtheir electron donor groups (amino groups) on the side of the ITOcoating and their electron accepting groups (nitro groups) on the sideof the aluminum electrode. This is achieved by applying a voltage V witha positive value to the ITO coating during the polarization phase. Moregenerally, for a polymer film of the same composition and differentthickness, the device will be polarized with a voltage V close to 100V/μm.

The photocell thus described generates a current of electrons to thealuminum electrode when it is illuminated with white light on itstransparent face.

The semiconductor device according to this invention also allows theproduction of an electroluminescent diode. A traditional way ofproducing an electroluminescent diode is described in the article “BlueLight Emitting Diodes with Doped Polymers” by E. GAUTIER, J. -M. NUNZI,C. SENTEIN, A. LORIN and P. RAIMOND published in Synthetic Metals, Vol.81, 1996, p. 197-200.

An electroluminescent diode according to this invention is showndiagrammatically in FIG. 6. Its structure is identical to that in FIG.4. It comprises a transparent substrate 30, for example made of glass,supporting a transparent electrode, for example an ITO electrode. Alayer of organic semiconductor 32 made up of a polymer including polarmolecules is between the transparent electrode 31 and a metal electrode33, for example made of aluminum. The electrodes 31 and 33 arerespectively connected to input terminals 34 and 35. In operation,light, indicated by arrows in FIG. 6, is emitted through the transparentface of the electroluminescent diode.

When the diode is subjected to a positive voltage on the transparentelectrode 31, charges are injected through the two electrodes 31 and 33into the polymer 32. On recombining, these charges emit light throughthe transparent face of the device. The electric field inside thestructure, which is induced by the orientation of the polar moleculescontained in the host polymer matrix, encourages the injection of thecharges and their recombination in +/− pairs in the polymer. In effect,this internal field restricts the direct transit, without recombination,of charges from one electrode to the other.

Electroluminescent diode structures can also be produced in accordancewith the device shown in FIG. 5. The thin organic film can be obtainedfrom a mixture of PMMA polymer at 30 g/l in 1,1,2-trichloroethane withthe DCM molecule at 5% by mass of PMMA (1.5 g/l of solution). Byfollowing the procedure previously described for the photocell in FIG.5, one can obtain organic films of 0.1 μm thickness. The aluminumelectrodes are then deposited as previously described. The polarizationof the device also takes place in the manner previously indicated.

The electroluminescent diode described emits red light at 620 nm throughthe transparent electrode when it is subjected to a voltage greater than20 V (positive on the transparent electrode).

Different embodiment variations can be envisaged within the scope ofthis invention. Hence, the active organic layer can be produced by amixture of different polymers and different molecules. Similarly, thesedifferent species can be chemically bonded (copolymer).

The transparent substrate can be ordinary glass but any othertransparent dielectric material is suitable, for example transparentplastics like polycarbonate and PMMA. These plastic materials allowflexible devices to be produced (in a sheet, in a roll, etc. . . . ).

So as to allow the passage of useful light, at least one of theelectrodes must be transparent. If, as in the case described, it is thesubstrate that is transparent, the electrode adjacent to this substratecan be made of indium oxide, mixed oxide of tin and indium or can beconstituted by a thin film of conductive polymer, that is transparentwithin the range of useful light, for example of the polyaniline type(Pani, distributed by Monsanto) or PEDT (distributed by Bayer), or itmay be constituted by a thin metal film (aluminum, gold, silver, . . . )deposited by evaporation and with a thickness close to 50 nm.

The upper electrode is advantageously a thin metal film deposited byevaporation (aluminum, gold, silver, magnesium, . . . ). According tothe type of device to be produced, this electrode can be opaque orsemi-transparent.

There are different techniques that allow a static electric field to beapplied to a thin film. One can polarize it using electrodes vaporizedonto the substrate and then onto the film. This is the method usedabove. This field can also be applied by depositing ions, created by aCorona effect close to a spike or a metal wire, onto the film, whichgenerally is highly resistive. This is the method that allows thecylinders of laser printers to be polarized. Polarization is alsopossible in the cold, when it is assisted optically.

The technique of polarization by electrodes consists of applying anelectric field by using electrodes positioned on each side of the film.The lower electrode can simply be a conductive substrate (doped siliconfor example), a metal electrode vaporized onto the substrate before thedeposition of the organic film or a transparent electrode (ITO)according to the type of device to be produced. The upper electrode is athin metal film deposited by vaporization.

Direct and accurate access to the value of the electric film applied tothe film constitutes the essential advantage of this method.Furthermore, this is a method that can be applied to the device as it isbeing produced. By bringing the material to a temperature close to itsvitreous transition temperature at the moment of polarization, themechanical stresses imposed by the polymer chains that constitute thematrix are reduced and this leads to the orientation of the dopingmolecules. It is then necessary to maintain the static field during thesample cooling phase before switching off at ambient temperature inorder to freeze the orientation of the molecules.

For certain molecule/polymer pairs, it is not necessary to heat theorganic layer to orientate the molecules. This is the case for DR1 inPVK. For other molecule/polymer pairs, orientation can be carried outwithout heating by application of a beam of light that is absorbed bythe molecules, this beam producing an effect equivalent to heating.

As has been previously stated, the polarization can also be carried outby a Corona effect. The application of an electrical potential on ametal surface with a small radius of curvature (a spike) results in thecreation of a high charge density per unit area at the convex interface.The electric flux is therefore concentrated close to this spike, leadingto ionization of a gas present close to the interface. The appearance ofions in the gas increases its conductivity and an electrical dischargeappears when the voltage applied to the gas exceeds the dielectricbreakdown voltage. Polarization by Corona effect consists of depositingthese ions onto the thin film in order to polarize them. The substratesto be used are the same as those used for the preceding method. Theupper metal electrode will then be deposited once the polarization hasbeen carried out.

It is also possible to produce the devices described above with areverse structure. In this case, the substrate and/or the lowerelectrode can be opaque. The upper electrode is then necessarilytransparent or semi-transparent. It can be produced by cathodicdeposition of ITO or by deposition of a thin metal film of thicknessclose to 10 to 50 nm (aluminum, gold, silver etc. . . . ). The advantageof such a type of device is that it can be produced by deposition on aflexible film of aluminum or Mylar® substrate (distributed by Dupont ofNemours). One then gains one production step; that relating to thedeposition of the lower electrode. The production of semiconductordevices other than electroluminescent diodes or photovoltaic cells alsocomes within the scope of this invention; for example, field effect typetransistors, such as the field effect transistor shown in FIG. 7, whoseactive semiconductor layer including a polymer layer 32 is constitutedand/or produced according to the characteristics of the invention. Inthis case, the increase in the mobility of the charge carriers inducedin accordance with the principle proposed is of great interest since thecharacteristics of the transistors (contrast between the on state andthe off state) depends greatly on this. The interest in organictransistors is that they permit the production of sensors (detectors anddosimeters).

What is claimed is:
 1. A semiconductor device comprising: a polymerhaving at least one rectifying function produced by a layer of thepolymer between first and second parallel electrodes, wherein: the layerof the polymer includes a host matrix for polar molecules, the polarmolecules are oriented perpendicular to the first and second electrodes,electrical charges of the polar molecules are aligned in a directiontowards the first and second electrodes, and said orientation of thepolar molecules induces an electric field inside the layer of thepolymer.
 2. A device according to claim 1, wherein said polar moleculesare molecules doping the host matrix.
 3. device according to claim 1,wherein said polar molecules are molecules grafted into the host matrix.4. A device according to claim 1, wherein said polar molecules have anelectron acceptor group and an electron donor group separated by one ormore groups comprising conjugated π electron systems.
 5. A deviceaccording to claim 1, wherein the host matrix is based on a polymerchosen from among polythiophene, polyparaphenylene,poly-paraphenylenevinylene, poly-methyl methacrylate, polyvinylcarbazole, polycarbonate, polystyrene and polyvinyl chloride.
 6. Adevice according to claim 1, further comprising: a substrate supportingthe first electrode, wherein at least one of the substrate, the firstelectrode, and the second electrode is transparent.
 7. A deviceaccording to claim 6, wherein the substrate supporting the firstelectrode comprises at least one of glass and plastic.
 8. A deviceaccording to claim 1, comprising: a conductive substrate used both as asupport and as the first electrode.
 9. A device according to claim 6,comprising: a photocell, said polar molecules including molecules of4-amino-4′-nitrobenzene.
 10. A device according to claim 6, comprising:an electroluminescent diode, said polar molecules including molecules of4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyrane. 11.Use of the semiconductor device according to claim 1 as a diode.
 12. Useof the semiconductor device according to claim 1 as anelectroluminescent diode.
 13. Use of the semiconductor device accordingto claim 1 as a photovoltaic diode.
 14. Use of the semiconductor deviceaccording to claim 1 as an active semi-conductive layer for a fieldeffect type transistor.